Centralize the selection of codec compilation flags to codec.make
to avoid having to duplicate the per cpu selection logic and the
build rule in the individual codec lib make files and make tweaking
easier.
The two special cases, libmad and libspeex were left alone.
I plan to introduce a var for arm generation so that appropriate flags
can be selected per generation as benchmarking results have shown that
different arm arches might have different optimal flags.
git-svn-id: svn://svn.rockbox.org/rockbox/trunk@30330 a1c6a512-1295-4272-9138-f99709370657
